<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        /* 必需 */
        .expand-transition {
            transition: all .3s ease;
            height: 30px;
            padding: 10px;
            background-color: #eee;
            overflow: hidden;
        }

        /* .expand-enter 定义进入的开始状态 */
        /* .expand-leave 定义离开的结束状态 */
        .expand-enter, .expand-leave {
            height: 0;
            padding: 0 10px;
            opacity: 0;
        }
    </style>
    <script>
        new Vue({
            el: '...',
            data: {
                show: false,
                transitionName: 'fade'
            }
        })
    </script>
</head>
<body>
<div v-if="show" transition="expand">hello</div>
</body>
</html>